1. Field of the Invention
The present invention relates to minimizing the destructive effects of non-reflected energy during lithography and, more particularly, to including a cooling system within a mask blank.
2. Description of the Related Art
In semiconductor lithography, and more specifically, extreme ultraviolet lithography (hereinafter xe2x80x9cEUVLxe2x80x9d), the desired pattern is imaged on top of a reflective substrate through an absorber layer by a mask or reticle. The reflective layer, however, has about a 70% reflectivity. Thus, the remaining non reflected energy, about 30%, is absorbed in the reflective substrate. Accordingly, during exposure, a large amount of heat is absorbed in the reticle substrate. The non-reflected energy in the reticle results in the reticle being heated, which causes the reticle to distort. Since the reticle illumination is non-telecentric, the distortion leads to large image placement variations on the wafer.
To overcome these distortions and variations, careful control of the reticle flatness and temperature, during the lithography, is required. Traditionally, a substrate material with a very low coefficient of thermal expansion and with a low flatness value is utilized, which results in minimizing the adverse effect of the non-reflected energy. However, materials that meet these standards are difficult to manufacturer and/or expensive. For example, the proposed SEMI specifications, SEMI standard 3148, as applied to EUVL is 5 ppb/C (for production class substrates) in combination with flatness requirements is extremely expensive to accomplish.
In order to attain the objects suggested above, there is provided, according to one aspect of the invention, an extreme ultraviolet (hereinafter xe2x80x9cEUVxe2x80x9d) mask comprising a cooling layer, wherein the cooling layer minimizes the distortion effects of nonreflected energy during lithography
In another embodiment of the present invention, there is provided a EUV mask wherein the mask comprises a substrate structure as a base for a reticle, a cooling layer, which is formed on the substrate structure; and a planarizing layer deposited on the cooling layer.
In another embodiment of the present invention, there is provided an EUV mask wherein the mask is cooled by a thermoelectric module.